TfL is reminding drivers that vehicles more than two metres (six foot six inches) wide are not permitted through the Rotherhithe Tunnel.
The safety of Londoners is TfL's top priority, which is why wide vehicles, generally vans or bigger, were banned from the tunnel in 2012.
Removing these vehicles from the tunnel reduces the risk of collisions, which have the potential to cause serious injuries to drivers and cause significant congestion in the surrounding area.
Glynn Barton, TfL's Director of Network Management, said: 'These restrictions are in place for very important reasons.
'This tunnel is more than a century old and was not designed for these types of vehicle so vans and wider vehicles risk colliding inside it, increasing road danger and disruption in the area.'
'We brought these restrictions in six years ago and we are reminding Londoners that they are there and why they are so important.'
As part of its regular monitoring of its network, TfL has identified that up to 6,500 vehicles wider than the restrictions could be illegally entering the tunnel every day, despite the clear signage on all approaches highlighting the restrictions.
Vehicles that use the tunnel illegally risk receiving a fine of £50 or prosecution.
Drivers restricted from the Rotherhithe Tunnel should use Tower Bridge or the Blackwall Tunnel - both of which are outside of the Congestion Charge.
For more information about driving in London, please visit tfl.gov.uk/traffic/status
Notes to editors